1. Field of the Invention
This invention relates to a device and method for superimposing and adding an time code information on, for example, a video signal, and a device and method for superimposing and adding a time code information and an additional information such as an anti-duplication control information in correlation to the time code information on a video signal.
2. Description of Related Art
The VTR (Video Tape Recorder) has been popularized, a lot of software which is reproducible using a VTR has been provided. Recently, digital playback devices such as digital VTRs and DVDs (Digital Video Disc) are now used practically, and pictures of good quality and sound of good quality can be easily played back and viewed.
However, on the other hand, the popularization gives rise to a problem that such abundant software are duplicated without any restriction, and heretofore various duplication prevention measures have been developed.
For example, though it is a method for inhibiting not directly duplication of analog video signals, a method in which the difference in AGC (Auto Gain Control) system or APC (Auto Phase Control) characteristics between a recording device such as a VTR and a monitor receiver for displaying a picture is utilized to prevent duplication substantially is available.
In detail, for example, a method in which a VTR performs AGC using a pseudo sync signal inserted in an video signal and a monitor receiver employs AGC system not using the pseudo sync signal is an example of the former method, and in the method, an extraordinarily high level pseudo sync signal is previously inserted as a sync signal for AGC when an analog video signal is recorded in an original recording medium, and then the extraordinarily high level pseudo sync signal is inserted in a video signal supplied from a playback VTR to a recording VTR as a sync signal for AGC.
A method utilizing the difference in APC characteristics in which the APC in a VTR follows a color burst signal in a video signal with a short time constant but the APC in a monitor receiver follows with a relatively long time constant is an example of the latter method, and in the method, the phase of a color burst signal of an video signal is previously inverted partially when analog video signals are recorded in an original recording medium, and then the video signal having the partially inverted color burst signal is outputted as a video signal supplied from a playback VTR to a recording VTR.
In the case described herein above, the monitor receiver which receives supply of the analog video signal from the playback VTR plays back a picture normally without receiving an adverse effect of the partial phase inversion of the color burst signal used for the pseudo sync signal and APC.
However, in the VTR which receives supply of the analog video signal having the inserted pseudo sync signal described herein above supplied from the playback VTR or subjected to the phase inversion control of the color burst signal and records the analog video signal in a recording medium, the VTR can not perform gain control or phase control based on the input signal, and records the video signal not normally. Therefore, a normal picture can not be viewed when the recorded video signal is played back.
In the case involving an analog video signal as described herein above, the duplication prevention method is not a method for inhibiting duplication, but a method for obtaining pictures which can not viewed normally, therefore it is said that this method is merely a passive duplication prevention control.
On the other hand, when digitized information, for example, a video signal is involved, a duplication prevention control signal including a duplication prevention code or a duplication generation control code is added to a video signal as a digital data and recorded in a recording medium in order to perform direct duplication prevention control, for example, duplication inhibition.
FIG. 1 is a fundamental structural diagram of a duplication device for processing this digitized information, and the device sends a digital video information played back by a digital playback device 200 to a digital record device 210 through a digital transmission channel 220, and plays back the digital video information if it is of duplication permitted and inhibits duplication if it is of duplication inhibited.
In a recording medium 201 mounted on the digital playback device 200, an anti-duplication control information is recorded in addition to the digital video information as an addition information. This anti-duplication control information indicates duplication prohibition, duplication permission, or generation limit as the control content. Digital reproduction unit 202 reads the digital information from the record medium 201, acquires the playback prevention control information with the digital video information, and sends it to the digital recording device 210 through digital transmission path 220.
The duplication prevention control signal detection unit 212 of the digital recording device 210 detects the duplication prevention control signal from the information which is received through the digital transmission path 220, and identifies the control contents. This identification result is transmitted to the digital recording unit 211.
If the identification result obtained from the duplication prevention control signal supplied from the duplication prevention control signal detection unit 212 is a signal which indicates the permission of recording of the digital video information inputted through the digital transmission path 220, the digital recording unit 211 converts the above-mentioned input digital video signal into a digital information suitable for recording, and writes it in a recording medium 213 to perform recording. On the other hand, if identification result obtained from duplication prevention control signal supplied from the duplication prevention control signal detection unit 212 is duplication inhibition, the digital record unit 211 does not perform record processing of the above-mentioned input digital video information.
If the identification result obtained from the duplication prevention control signal supplied from the duplication prevention control signal detection unit 212 is a signal which permits only the first generation duplication, the digital record unit 211 converts the above-mentioned input digital signal into digital video information suitable for recording, writes it in the recording medium 213, and performs recording, and it changes the anti-duplication control signal used as an addition information to a signal for indicating duplication inhibition (duplication inhibition of the next generation), and records it in the recording medium 213. Accordingly, the video signal cannot be duplicated using the duplicated recording medium 213
As described herein above, in the case of so-called digital connection for supplying a video signal as major information signal and an anti-duplication control signal as an addition information to a recording device in the form of a digital signal, because an anti-duplication control signal is included in the transmitted digital data, the recording device performs duplication prevention control such as duplication inhibition using this anti-duplication control signal consistently.
In the case that the digital playback device of FIG. 1 is, for example, a digital VTR, the digital VTR converts only the video signal namely the major information signal and sound signal into an analog signal through a D/A conversion circuit 203 in order to monitor the played back video signal and sound signal, and guides it to the analog output terminal 204, to which usually a monitor television set is connected.
As described herein above, even though a playback device for digital information is involved, the anti-duplication control signal is not included in the analog signal guided to the analog output terminal 204. Hence, in the case of analog connection that analog VTR is connected to the analog output terminal 204, the information signal is duplicated undesirably.
So it comes to mind that an anti-duplication control signal is superimposed and added to the D/A converted video signal and sound signal, however it is difficult to add the anti-duplication control signal, to extract it in the recording device, and to use it for duplication prevention control without deterioration of the D/A converted video signal and sound signal.
Accordingly, heretofore, only the way to prevent duplication in the case of analog connection has been the passive duplication prevention method which utilizes the above-mentioned difference of AGC system between a VTR and monitor television set or the above-mentioned difference of characteristics of APC.
However, in the case of the above-mentioned duplication prevention control method which utilizes difference of AGC system between a VTR and monitor television set or difference of characteristics of APC, it can happen that the video signal is recorded normally, that is, even the passive duplication prevention can not be performed depending on the AGC system or APC characteristics of the recording device side. Further, the method can cause a problem that a playback picture displayed on the monitor television set is abnormal.
As a duplication prevention control system which is used effectively for either analog connection and digital connection while the above-mentioned problems are solved without deterioration of a played back video signal and sound signal, the inventors of this invention proposed previously a method in which an anti-duplication control signal is spectrally spread, the spectrally spread anti-duplication control signal is superimposed on a video signal, and the video signal is recorded as a digital signal or an analog signal (refer to Japanese Patent Application No.-Hei-339959, UP Patent Application No. 08/755101). 
In this system, a PN (Pseudorandom Noise) series code used as a spread code (referred to as PN code hereinafter) is generated with a sufficiently short period, and spectral spread is performed by multiplying the anti-duplication control signal by the PN code, and then the narrow-band high level anti-duplication control signal is converted into a wide-band low level signal which does not adversely affect the video signal and sound signal, and the spectrally spread anti-duplication control signal superimposed on an analog video signal is recorded in a recording medium. In this case, the signal to be recorded in the recording medium may be either a video signal or digital signal.
In this system, because the anti-duplication control signal is superimposed on a video signal as a spectrally spread wide-band low level signal, it is difficult for the person who wants to duplicate illegally to remove the superimposed anti-duplication control signal from video signal.
On the other hand, it is possible to detect and use the superimposed anti-duplication control signal by performing inverse spectral spread. Accordingly the anti-duplication control signal is provided to the recording device side with the video signal surely, and in the recording device side, the anti-duplication control signal is detected, and the duplication control corresponding to the detected anti-duplication control signal can be performed surely.
By the way, to superimpose the anti-duplication control signal namely the additional information on the video signal by the above-mentioned spectral spread system without deterioration of the playback picture, it is required that the additional information spectrally spread with a sufficiently low level for causing no deterioration of the S/N ratio of the video signal is superimposed on the video signal. In order to obtain such level, it is required that the code length of the spectrally spreading PN code is sufficiently long.
But when the code length is long as described herein above, a method in which a matched filter is used or sliding correlation is used can not be used practically as a synchronizing method for matching the phase of the inverse spreading PN code to that of the spreading PN code when spectrally spreading because it takes very long time for synchronizing.
It is considered that the spectrally spreading PN code string is generated synchronously to the video sync signal, because the PN code string which was used in reverse spreading is obtained easily only by generating a PN code string synchronously to a video sync signal. The additional information can be superimposed relatively easily without deterioration of the video signal as described above if a PN code having a long period of a plurality of fields is used as the PN code having a sufficiently long code length.
However, because time code information for indicating time continuity is not added usually to a video signal, there is no means to estimate the relation to the field, fields adjacent to a frame, or a frame. To generate a PN code over a plurality of fields more than two or over a plurality of frames, it is required that a means for identifying synchronization of a unit of the plurality of fields or the plurality of frames is used separately, and as such means, a method in which information for synchronizing to the spectral spread code is inserted and added in the vertical blanking period of the video signal is considered possible to be applied.
However information of a vertical blanking period is not transmitted usually when a video signal is transmitted as a digital signal. Hence, sync information of spectral spread is transmitted as a digital additional information in addition to the digital video signal, however, in the case of analog connection in which the above-mentioned digital information is D/A converted and outputted, the sync information is eliminated. To avoid this problem, in the case of analog connection, the sync information of spectral spread is generated again from the time code provided as the digital additional information, and inserted and added in the vertical blanking period of the analog video signal, however such troublesome operation is disadvantageous.
When an additional information is spectrally spread using the spectral spread code spread over a plurality of fields or a plurality of frames, in the case of a method for detecting synchronization in which synchronization is detected by merely indicating the head position, if field data was eliminated by field thinning processing or field data was inserted by field interpolation processing, and the method results in changing of the synchronizing phase to lead no synchronization of the PN code for inverse spread because such elimination or insertion of the field data is not detected.
In the case that the additional information is an anti-duplication control signal, such result means that the anti-duplication control signal is changed by the above-mentioned method.
In view of the above-mentioned problems, it is an object of the present invention to provides a method and device for superimposing surely a time code for indicating time continuity of the picture on the video signal regardless that the video signal is an analog video signal or a digital video signal.
It is another object of the present invention to provide a method and device in which, for example, an additional information such as an anti-duplication signal is spectrally spread and superimposed on an interval which continues over a plurality of fields or a plurality of frames of the video signal, and is detected easily.
The method for adding information to a video signal of the present invention comprises a step for generating a timing signal based on a sync signal of the video signal, a step for periodically generating a time code information signal synchronously to the timing signal, a step for periodically generating a first spectral spread code string synchronously to the timing signal, a step for generating a second spectral spread code string correspondingly to the time code information signal synchronously to the timing signal, a step for generating a spread time code signal by spectrally spreading the time code information signal using the first spectral spread code string, a step for generating a spread additional information signal by spectrally spreading an additional information signal using the second spectral spread code string, and a step for adding the spread time code signal and the spread additional information signal to the video signal.
According to the present invention, it is possible to make illegal alteration processing more difficult in the case that the additional information is a secret information such as an anti-duplication control signal.